The present invention relates to technology for arbitration for a bus mastership in a bus system wherein data are transmitted and received among a plurality of modules through a bus.
Known as an apparatus which utilizes a bus system wherein data are transmitted and received among a plurality of modules through a bus is, for example, an ATM multiplexer wherein data sent from a plurality of non-ATM (Asynchronous Transfer Mode) lines are turned into ATM cells so as to transmit the ATM cells onto an ATM line, while ATM cells sent from the ATM line are decellularized into data so as to transmit the data to the plurality of non-ATM lines.
In such an ATM multiplexer, a non-ATM line interface module which accommodates the non-ATM lines, and an ATM line interface module which accommodates the ATM line are interconnected by the bus. Using the bus, the ATM cell sent from the ATM line is received and is transmitted to the non-ATM line interface module by the ATM line interface module, or the data sent from the non-ATM line are received and turned into the ATM cell by the non-ATM line interface module so as to transmit the ATM cell to the ATM line interface module.
In the ATM multiplexer as stated above, arbitration for a bus mastership for granting the use of the bus to only one interface module in a case where the plurality of interface modules simultaneously made requests for the use of the bus in order to transmit the ATM cells has heretofore been implemented merely by allowing the respective interface modules to use the bus in a predetermined sequence.
Since such arbitration for the bus mastership performs the priority control of the bus mastership in interface module units, it cannot perform the priority control of the bus mastership in accordance with the priority degrees of the ATM cells themselves to be transmitted or received on the bus. Therefore, the bus use of the ATM cell to be primarily transmitted in preference is postponed to that of the ATM cell of lower priority degree. This results in the problem that the transmission of the primarily preferential ATM cell to the line delays.
The problem is not limited only to the ATM multiplexer. It similarly arises in, for example, an IP multiplexer wherein data sent from a plurality of non-IP (Internet Protocol) lines are turned into IP packets so as to transmit the IP packets to an IP line, while data are derived from IP packets sent from the IP line so as to transmit the data to the plurality of non-IP lines.